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In comparison with forged steel, the Pearlitic Ductile Iron (PDI) for diesel engine crankshaft is limited by its low bending fatigue strength. Nitriding followed by fillet deep rolling introduced in this paper is proved to be an effective way to improve the fatigue properties. Two types of crankshafts of turbocharged and intercooled diesel engines were investigated with this method. The PDI material used in both cases was as-cast QT700-2 with a nominal tensile strength of 700MPa and elongation no less than 2%. Bending fatigue tests have shown that the bending fatigue limits of the duplex treated PDI crankshafts were equivalent to those of the fillet hardened steel ones. The feasibility of the application of the duplex treated PDI to the medium-and heavy-duty diesel engine crankshafts has been validated by the results of users' road tests as well as engine tests.

The traditional Up And Down Method (UADM) is generally taken as a standard mean to determine the fatigue limit of an automotive component. Its main draw back is extremely time-consuming. A number of other methods can reduce testing time to some extent, but the applications of those results are limited, since they are not comparable with that of UADM. Based on certain preconditions and assumptions, an accelerated testing method, named Fixed Emitting Point Method, has been developed. The applicability and effectiveness of this method have been verified by bending fatigue test of crankshaft and tension-compression fatigue test of connecting rod. Results showed that the errors in the mean fatigue limit values are generally less than 5% while the number of cycles of a test can be reduced by about 90% in comparison with the data given by UADM.

Component fatigue test is extremely time-consuming and costly. In order to get more reliable test results in a shorter period, a computerized electrodynamic resonant fatigue test machine, named PDC model, has been developed and applied to automotive component tests at Dong Feng Motor Co. Ltd. It can be divided into two major parts: a mechanical resonant rig and a computerized electronic control system. In this paper the structure and working principle of the machine is described, the characteristic of the resonant system is analyzed and the load calibration method of the machine is also dealt with. In addition to bending fatigue test of crankshaft □ the typical applications of the PDC are torsional and bending-torsional complex fatigue tests of crankshaft, torsional fatigue test of small bars and standard material specimen, bending fatigue test of semi-axle sleeve and compressive fatigue test for valve spring.